Tree diversity as a control of whole tree water use in experimentally assembled mixtures in Panama

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As natural tropical forests diminish and former rain forest areas are being degraded, more tropical tree plantations may be established. Up to now, they usually consist of a single exotic fast growing species. There is much, and recently increasing concern about high water use rates and non-sustainable soil nutrient depletion by such plantations. Recent approaches to reforestation in the tropics emphasize the establishment of native species in mixed stands. In an experimental plantation in Panama, native tree species, which in natural forest exhibit different relative growth rates, were planted at different diversity levels. The proposed project intends to analyze the whole tree water use of these species in plots of different diversity levels (1-, 3-, and 6-species mixtures), and to analyze the soil water partitioning among cooccurring species. The methods include soil hydrological measurements, tree sap flux analyses and the application of stable isotope techniques (¿D). We plan to cooperate closely with a project studying the tree nutrient budget. Overall, we wish to increase the knowledge for an ecologically sound reforestation of degraded tropical areas with respect to tree species diversity and water and nutrient resources.